Hydraulic couplers for quickly connecting and disconnecting attachments, such as buckets, from excavating and construction equipment are well known. By way of example, such attachments are usually attached to an arm of the excavator using two spaced and parallel pins provided on the attachment, wherein one of the pins is generally located in an open-mouthed substantially C-shaped aperture of the coupling and the other pin is located in a similar C-shaped aperture, one or both of the pins being secured within the respective C-shaped aperture by means of a movable jaw or latch member. The C-shaped apertures are arranged such that when the first pin is located in the first aperture and the second pin is secured in the second aperture and the or each latch member is closed the attachment is securely held by the coupling. Typically the or each moveable latch member is moved between an open and a closed position by means of a double acting hydraulic ram operated by a hydraulic control system.
There are many prior art examples of control systems for controlling the operation of such hydraulic couplers, but all have an inherent problem in that a failure of the hydraulic ram supplying primary locking force to the or each latch member can go undetected, possibly causing the attachment to swing or even completely detach from the coupler, posing a serious safety hazard. A similar hazard can occur should the hydraulic pipes supplying the coupler become damaged. The most common area for damage is at the connection between the excavator dipper arm and the coupler. Here the hydraulic hoses are continually flexed and are prone to damage causing premature wear and failure. The failure of a hydraulic hose also leads to the loss of hydraulic oil which also can pollute the environment.
Normally the control system consists of a 4/2 solenoid/spring valve fed with pressurised hydraulic oil from either the excavator main hydraulic line or the excavator servo (reduced pressure) hydraulic line. From the valve two high pressure hydraulic pipes, either flexible or a mixture of flexible and rigid, run from the engine compartment, up the excavator boom, unsupported across the excavator boom to dipper connection, down the dipper arm, unsupported across the excavator dipper to coupler, and terminate at the hydraulic ram within the coupler body. Normally these pipes are split into shorter lengths to facilitate replacement in the event of a failure. In the event of a pipe rupture or an internal failure of the ram the driver has no indication.